Well, 8820, I'd say the machine of your namesake holds the record [as far as I have seen] of the longest-lasting combine, ever!
A friend of mine, a custom harvester, put over 12,000 hours on one and over 13,500 on another before finally retiring them. Much of the original sheet metal had been replaced. Their engines had at least 1 full overhaul. The separators were completely overhauled seasonally.
I think one secret to my friend's success is also the fact, the 8820's were completely stripped to the shell and re-assembled piece by piece in his shop. It was a lot of extra work, sure, but my friend was never sold on a factory-built combine, always telling me how it just as easily could have been cobbled together on a Monday after a holiday!
His 8820's were as sound, strong and healthy from the get-go. I believe to this day, that was the right start toward their 13,000-hour lives.